Process for producing polycarbonate

ABSTRACT

Provided is a process for producing a polycarbonate, which comprises preparing a polycarbonate prepolymer through prepolymerization followed by polymerizing the prepolymer in a solid phase in the presence of a phosphorus-containing basic compound serving as a catalyst in an atmosphere of a poor solvent gas. Preferably, the poor solvent is one in which the polycarbonate has a solubility of at most 0.1% by weight, more preferably, a linear aliphatic or cycloaliphatic hydrocarbon having from 5 to 18 carbon atoms. The process is efficient in producing high-quality polycarbonates having a high molecular weight.

TECHNICAL FIELD

The present invention relates to a process for producing polycarbonates.More precisely, it relates to an efficient process for producinghigh-quality polycarbonates having a high molecular weight.

BACKGROUND ART

For producing polycarbonates, known are a method of directly reacting anaromatic dihydroxy compound such as bisphenol A or the like withphosgene (interfacial polycondensation), and a method oftransesterifying an aromatic dihydroxy compound such as bisphenol A orthe like with a dicarbonate such as diphenyl carbonate or the like in amelt or solid phase (melt polymerization, solid-phase polymerization).

The interfacial polycondensation method is problematic in that itrequires toxic phosgene and the chlorine-containing side products formedcorrode the apparatus used. On the other hand, the melt polymerizationmethod in which the monomers are reacted for a long period of time athigh temperatures generally falling between 280° C. and 310° C. is alsoproblematic in that the polycarbonates produced are inevitably coloredand could not have a high molecular weight.

To solve the problems with the melt polymerization method, one proposalwas made in Japanese Patent Laid-Open No. 208823/1996. The methodproposed comprises polymerizing the prepolymer for the intendedpolycarbonate in a poor solvent gas stream in the presence of anitrogen-containing organic basic catalyst. In that method, thepolycarbonate produced could have good quality but could not have asufficiently increased molecular weight. The method could not stillsolve the outstanding problem of how to produce high-molecular-weightpolycarbonates.

To produce high-molecular-weight polycarbonates, another method wasproposed, which comprises preparing a polycarbonate prepolymer followedby polymerizing it in a solid phase and in which the prepolymer beingpolymerized is in a swollen solid phase in a swelling solvent gas stream(Japanese Patent Laid-Open No. 235368/1997). In that method, however,polycarbonates having a sufficiently increased molecular weight couldnot still be obtained. What is more, the method is problematic in that,when the polymerization temperature is further elevated so as toincrease the molecular weight of the polycarbonate being produced, thenthe polycarbonate produced dissolves in the swelling solvent used.

In the laid-open patent specification, also proposed was solid-phasepolymerization of the prepolymer in an atmosphere of nitrogen gas orlower hydrocarbon gas. However, this is not favorable since theefficiency of trapping the phenolic side products formed duringpolymerization is poor and the side products are difficult to separate,remove and recover.

The object of the present invention is to solve the problems with theconventional polycarbonate production methods as above and to provide anefficient process for producing high-quality polycarbonates having ahigh molecular weight.

DISCLOSURE OF THE INVENTION

We, the present inventors have assiduously studied so as to attain theobject as above, and, as a result, have found that, when a polycarbonateprepolymer (this may be hereinafter simply referred to as “prepolymer”)is prepared and polymerized in a solid phase in the presence of aspecific catalyst and in a specific solvent atmosphere, then the objectcan be attained.

The present invention has been accomplished on the basis of thisfinding.

Specifically, the invention provides the following:

(1) A process for producing a polycarbonate, which comprises preparing apolycarbonate prepolymer through prepolymerization followed bypolymerizing the prepolymer in a solid phase in the presence of aphosphorus-containing basic compound serving as a catalyst in anatmosphere of a poor solvent gas.

(2) The process for producing a polycarbonate of above (1), wherein thepoor solvent is one in which the polycarbonate has a solubility of atmost 0.1% by weight.

(3) The process for producing a polycarbonate of above (1), wherein thepoor solvent is a linear aliphatic or cycloaliphatic hydrocarbon havingfrom 5 to 18 carbon atoms.

(4) The process for producing a polycarbonate of any one of above (1) to(3), wherein the phosphorus-containing basic compound is a quaternaryphosphonium salt.

BEST MODES OF CARRYING OUT THE INVENTION

The starting materials for producing polycarbonates in the invention arenot specifically defined. Preferably used are (A) dihydroxy compoundsand (B) dicarbonates or phosgene, and optionally used areterminal-stopping agents, chain-branching agents, etc. These startingmaterials are prepolymerized to give prepolymers, which are thenpolymerized in a solid phase into polycarbonates.

The catalyst in prepolymerization is not specifically defined, butpreferred is a nitrogen-containing organic basic compound. In thesolid-phase polymerization, used is a phosphorus-containing basiccompound, preferably a quaternary phosphonium salt.

(1) Starting Materials:

Dihydroxy compounds for component (A):

For example, aromatic dihydroxy compounds and aliphatic dihydroxycompounds are mentioned, and at least one selected from them is used inthe invention.

As examples of the aromatic dihydroxy compounds usable as the component(A), mentioned are those of a general formula (1):

In formula (1), R¹ and R² each represent a halogen atom such as afluorine, chlorine, bromine or iodine atom, or an alkyl group havingfrom 1 to 8 carbon atoms such as a methyl, ethyl, n-propyl, isopropyl,n-butyl, isobutyl, sec-butyl, t-butyl, pentyl, hexyl, cyclohexyl, heptylor octyl group. R¹ and R² may be the same or different ones. PluralR¹'s, if any, may be the same or different ones; and plural R²'s, ifany, may be the same or different ones. m and n each represent aninteger of from 0 to 4. Z represents a single bond, an alkylene grouphaving from 1 to 8 carbon atoms, an alkylidene group having from 2 to 8carbon atoms, a cycloalkylene group having from 5 to 15 carbon atoms, acycloalkylidene group having from 5 to 15 carbon atoms, or a bond of—S—, —SO—, —SO₂—, —O— or —CO—, or a bond of the following formula (2) or(3):

The alkylene group having from 1 to 8 carbon atoms and the alkylidenegroup having from 2 to 8 carbon atoms include, for example, methylene,ethylene, propylene, butylene, pentylene, hexylene, ethylidene andisopropylidene groups. The cycloalkylene group having from 5 to 15carbon atoms and the cycloalkylidene group having from 5 to 15 carbonatoms include, for example, cyclopentylene, cyclohexylene,cyclopentylidene and cyclohexylidene groups.

In preferred embodiments of the invention, one or more of the compoundsmentioned above are suitably selected and used as the dihydroxycompounds for the component (A). Of those compounds noted above,preferred is an aromatic dihydroxy compound, bisphenol A.

In addition, diesters of dihydroxy compounds, dicarbonates of dihydroxycompounds, and monocarbonates of dihydroxy compounds are also usable inthe invention.

Compounds for component (B):

[1] Dicarbonates:

Various types of dicarbonates are usable in the invention. For example,used is at least one selected from diaryl carbonates, dialkyl carbonatesand alkylaryl carbonates.

The diaryl carbonates usable for the component (B) include compounds ofa general formula (4):

wherein Ar¹ and Ar² each represent an aryl group, and these may be thesame or different ones;

and compounds of a general formula (5):

wherein Ar³ and Ar⁴ each represent an aryl group, and these may be thesame or different ones; and D¹ represents a residue of an aromaticdihydroxy compound of those of formula (1) noted above from which twohydroxyl groups are removed.

The dialkyl carbonates include compounds of a general formula (6):

wherein R³ and R⁴ each represent an alkyl group having from 1 to 6carbon atoms or a cycloalkyl group having from 4 to 7 carbon atoms, andthese may be the same or different ones;

and compounds of a general formula (7):

wherein R⁵ and R⁶ each represent an alkyl group having from 1 to 6carbon atoms or a cycloalkyl group having from 4 to 7 carbon atoms, andthese may be the same or different ones; and D² represents a residue ofan aromatic dihydroxy compound of those noted above from which twohydroxyl groups are removed.

The alkylaryl carbonates include compounds of a general formula (8):

wherein Ar⁵ represents an aryl group; and R⁷ represents an alkyl grouphaving from 1 to 6 carbon atoms or a cycloalkyl group having 4 carbonatoms;

and compounds of a general formula (9):

wherein Ar⁶ represents an aryl group; R⁸ represents an alkyl grouphaving from 1 to 6 carbon atoms or a cycloalkyl group having from 4 to 7carbon atoms; and D³ represents a residue of an aromatic dihydroxycompound of those noted above from which two hydroxyl groups areremoved.

One or more of the compounds mentioned above are suitably selected andused as the dicarbonates for the component (B) Of those compounds notedabove, preferred is diphenyl carbonate.

[2] Phosgene:

Phosgene may be used for the component (B). Phosgene, if used, requiresa suitable amount of a monohydroxy compound.

(2) Prepolymerization to Prepare Prepolymers:

The starting materials, dihydroxy compound for the component (A), anddicarbonate or phosgene for the component (B) are prepolymerizedoptionally along with a terminal-stopping agent or a chain-branchingagent to prepare prepolymers. In this step, preferably used is anitrogen-containing organic basic compound serving as a catalyst.

Preferred methods and conditions for prepolymerization are describedconcretely.

[1] Methods for Prepolymerization:

(i) A dihydroxydiaryl compound may be reacted with a diaryl carbonateunder heat to give a prepolymer while the aromatic monohydroxy compoundresulting from the reaction is removed. The viscosity-average molecularweight of the prepolymer to be prepared in this prepolymerization steppreferably falls between 2000 and 20000. It is desirable that theprepolymerization is effected in melt.

The ratio of the diaryl carbonate to the dihydroxydiaryl compound to bereacted (that is, to be fed into the reactor) varies, depending on thetype of the compounds, the reaction temperature and also other reactionconditions, but may fall generally between 0.9 and 2.5.

The reaction temperature and the reaction time also vary, depending onthe type and the amount of the starting compounds and the catalyst used,the intended degree of prepolymerization of the prepolymer to beprepared, and other reaction conditions. Preferably, the reactiontemperature falls between 50 and 350° C., and the reaction time fallsbetween 1 minute and 100 hours. In order that the prepolymer prepared isnot colored, it is desirable that the temperature for theprepolymerization is as low as possible and the time for it is as shortas possible. The pressure during the reaction preferably falls between 1Torr and 5 kg/cm²G.

The terminal ratio of the prepolymer to be prepared in this steppreferably falls between 50/50 and 99/1 in terms of the ratio of phenylcarbonate terminal/hydroxyl terminal.

(ii) An aromatic dihydroxy compound may be reacted with phosgene to givea prepolymer in any known manner in the presence of a molecularweight-controlling agent, an acid-binding agent and a solvent such asthose mentioned above.

[2] Catalysts for Prepolymerization:

Catalysts for the prepolymerization are not specifically defined, butpreferred are nitrogen-containing organic basic compounds which will bedescribed hereunder. In the prepolymerization step, it is desirable thatthe catalyst of a nitrogen-containing organic basic compound is used inan amount of from 10⁻⁸ to 10⁻² mols, more preferably from 10⁻⁷ to 10⁻³mols, relative to one mol of the starting dihydroxy compound of thecomponent (A). If the amount of the nitrogen-containing organic basiccompound used is smaller than 10⁻⁸ mols, the catalytic activity in theinitial stage of the reaction will be low. However, if larger than 10⁻²mols, the cost of the catalyst unfavorably increases. As the case maybe, in this stage, one or more of the polymerization catalysts to bementioned hereinunder may be used either singly or as combined.

Various types of nitrogen-containing organic basic compounds areemployable herein with no specific limitation. For example, employableare aliphatic tertiary amine compounds such as trimethylamine,triethylamine, tripropylamine, tributylamine, tripentylamine,trihexylamine, dimethylbenzylamine, etc.; aromatic tertiary aminecompounds such as triphenylamine, etc.; and nitrogen-containingheterocyclic compounds such as N,N-dimethyl-4-aminopyridine,4-diethylaminopyridine, 4-pyrrolidinopyridine, 4-aminopyridine,2-aminopyridine, 2-hydroxypyridine, 4-hydroxypyridine,2-methoxypyridine, 4-methoxypyridine, imidazole, 2-methylimidazole,4-methylimidazole, 2-dimethylimidazole, 2-methoxyimidazole,2-mercaptoimidazole, aminoquinoline, diazabicyclooctane (DABCO), etc. Inaddition, further employable are quaternary ammonium salts of a generalformula (10):

(NR⁹ ₄)⁺(X¹)⁻  (10).

In formula (10), R⁹ represents an organic group, for example, an alkylor cycloalkyl group such as a methyl, ethyl, propyl, butyl, pentyl,hexyl, octyl or cyclohexyl group, an aryl group such as a phenyl, tolyl,naphthyl or biphenyl group, or an arylalkyl group such as a benzylgroup. Four R⁹'s may be the same or different ones; and two of them maybe bonded to each other to form a cyclic structure. X¹ represents ahalogen atom, a hydroxyl group, or BR₄, in which R represents a hydrogenatom, or a hydrocarbon group such as an alkyl or aryl group, and fourR's may be the same or different ones.

Examples of the quaternary ammonium salts include, for example, ammoniumhydroxides having alkyl, aryl and/or alaryl groups, such astetramethylammonium hydroxide, tetraethylammonium hydroxide,tetrabutylammonium hydroxide, trimethylbenzylammonium hydroxide, etc.;and basic salts such as tetramethylammonium borohydride,tetrabutylammonium borohydride, tetrabutylammonium tetraphenyl borate,tetramethylammonium tetraphenyl borate, etc.

Of the nitrogen-containing organic basic compounds noted above,preferred are the quaternary ammonium salts of formula (I), concretelysuch as tetramethylammonium hydroxide, tetrabutylammonium hydroxide,tetramethylammonium borohydride, and tetrabutylammonium borohydride,since they have high catalytic activity and since they are easilypyrolyzed and hardly remain in the polymers produced. Of those,especially preferred is tetramethylammonium hydroxide.

One or more of these nitrogen-containing organic basic compounds areemployable herein either singly or as combined.

It is desirable that the amount of metallic impurities in thenitrogen-containing organic basic compounds for use in the invention isas small as possible. Especially preferably, the amount of alkali metaland alkaline earth metal compounds in those compounds is not larger than50 ppm.

[3] Crystallization of Prepolymers:

The prepolymers thus prepared herein are preferably crystallized, forwhich the method is not specifically defined. Preferred is solventtreatment for crystallization or crystallization under heat.

(3) Polymerization to Produce Polycarbonates:

In the invention, the polycarbonate prepolymer prepared is thenpolymerized in a solid phase in the presence of a phosphorus-containingbasic compound serving as a polymerization catalyst, preferably aquaternary phosphonium salt.

[1] Catalysts for Polymerization:

(a) Phosphorus-containing Basic Compounds:

One or more phosphorus-containing basic compounds are usable eithersingly or as combined.

(i) Tri-valent Phosphorus Compounds:

Various tri-valent phosphorus compounds are usable herein with nospecific limitation. For example, used are compounds of general formulae(11) and (12):

R⁹ ₃P  (11)

(R⁹O)₃P  (12).

In formulae (11) and (12), R⁹ represents a hydrogen atom or an organicgroup. The organic group includes, for example, an alkyl or cycloalkylgroup such as a methyl, ethyl, propyl, butyl, pentyl, hexyl, octyl orcyclohexyl group; an aryl group such as a phenyl, tolyl, naphthyl orbiphenyl group; and an arylalkyl group such as a benzyl group. ThreeR⁹'s may be the same or different ones, or two of them may be bonded toeach other to form a cyclic structure.

Of those tri-valent phosphorus compounds, the compounds of formula (11)include, for example, alkylphosphines such as ethylphosphine,diethylphosphine, propylphosphine, etc.; and arylphosphines orarylalkylphosphines such as phenylphosphine, diphenylphosphine,phenylmethylphosphine, etc. The compounds of formula (12) include, forexample, alkyl phosphites such as dimethyl phosphite, trimethylphosphite, diethyl phosphite, triethyl phosphite, dibutyl phosphite,etc.; aryl phosphites such as diphenyl phosphite, triphenyl phosphite,tris(ethylphenyl) phosphite, etc.; and arylalkyl phosphites such asdiphenyloctyl phosphite, diphenyldecyl phosphite, phenyldidecylphosphite, etc.

(ii) Quaternary Phosphonium Salts:

Various quaternary phosphonium salts are usable herein with no specificlimitation. For example, preferably used are compounds of generalformulae (13) and (14):

(PR¹⁰ ₄)⁺(X¹)⁻  (13)

(PR¹⁰ ₄)₂ ⁺(Y¹)²⁻  (14).

In formulae (13) and (14), R¹⁰ represents an organic group. The organicgroup includes, for example, an alkyl or cycloalkyl group such as amethyl, ethyl, propyl, butyl, pentyl, hexyl, octyl orcyclohexyl group;an aryl group such as a phenyl, tolyl, naphthyl or biphenyl group; andan arylalkyl group such as a benzyl group. Four R¹⁰'s may be the same ordifferent ones, or two of them may be bonded to each other to form acyclic structure. X¹ represents a group capable of forming a mono-valentanion, such as a halogen atom, a hydroxyl group, an alkyloxy group, anaryloxy group, R′COO, HCO₃, (R′O)₂P(═O)O, BR″₄ or the like. In those, R′represents a hydrocarbon group such as an alkyl group, an aryl group orthe like, and two (R′O) s may be the same or different ones. R″represents a hydrogen atom, or a hydrocarbon group such as an alkylgroup, an aryl group or the like, and four R″s may be the same ordifferent ones. Y¹ represents a group capable of forming a di-valentanion, such as CO₃ or the like.

The quaternary phosphonium salts include, for example, tetra(aryl oralkyl)phosphonium hydroxides such as tetraphenyl phosphonium hydroxide,tetranaphthylphosphonium hydroxide, tetra(chlorophenyl)phosphoniumhydroxide, tetra (biphenyl)phosphonium hydroxide, tetratolylphosphoniumhydroxide, tetramethylphosphonium hydroxide, tetraethylphosphoniumhydroxide, tetrabutylphosphonium hydroxide, etc.; as well astetramethylphosphonium tetraphenyl borate, tetraphenylphosphoniumbromide, tetraphenylphosphonium phenolate, tetraphenylphosphoniumtetraphenyl borate, methyltriphenylphosphonium tetraphenyl borate,benzyltriphenylphosphonium tetraphenyl borate,biphenyltriphenylphosphonium tetraphenyl borate, tetratolylphosphoniumtetraphenyl borate, tetraphenylphosphonium phenolate,tetra(p-t-butylphenyl)phosphonium diphenyl phosphate,triphenylbutylphosphonium phenolate, triphenylbutylphosphoniumtetraphenyl borate, etc.

Except the compounds of formulae (13) and (14) noted above, also usableherein are bis-tetraphenylphosphonium salt of2,2-bis(4-hydroxyphenyl)propane, and ethylenebis(triphenylphosphonium)dibromide, trimethylenebis(triphenylphosphonium)-bis(tetraphenylborate), etc.

Of the quaternary phosphonium salts noted above, preferred are thosehaving alkyl groups, since they have high catalytic activity and sincethey are easily pyrolyzed and hardly remain in the polymers produced.For example, preferably used are tetraphenylphosphonium tetraphenylborate, tetrabutylphosphonium tetraphenyl borate, tetraethylphosphoniumtetraphenyl borate, etc.

Further usable herein are quaternary phosphonium salts having aryland/or branched alkyl groups, for example, tetraphenylphosphoniumhydroxide, tetranaphthylphosphonium hydroxide,tetra(chlorophenyl)phosphonium hydroxide, etc.; mono(aryl oralkyl)triphenylphosphonium hydroxides such as methyltriphenylphosphoniumhydroxide, ethyltriphenylphosphonium hydroxide,propyltriphenylphosphonium hydroxide, etc.;mono(aryl)trialkylphosphonium hydroxides such asphenyltrimethylphosphonium hydroxide, biphenyltrimethylphosphoniumhydroxide, etc.; diaryldialkylphosphonium hydroxides such asdimethyldiphenylphosphonium hydroxide, etc.; tetraarylphosphoniumtetraphenyl borates such as tetraphenylphosphonium tetraphenyl borate,tetranaphthylphosphonium tetraphenyl borate, etc.; mono (aryl oralkyl)triphenylphosphonium tetraphenyl borates such asmethyltriphenylphosphonium tetraphenyl borate, ethyltriphenylphosphoniumtetraphenyl borate, etc.; monoaryltrialkylphosphonium tetraphenylborates such as phenyltrimethylphosphonium tetraphenyl borate,biphenyltrimethylphosphonium tetraphenyl borate, etc.;diaryldialkylphosphonium tetraphenyl borates such asdimethyldiphenylphosphonium tetraphenyl borate,diethyldiphenylphosphonium tetraphenyl borate, etc.

In the quaternary phosphonium salts noted above for use herein, thecounter anion of hydroxide or tetraphenyl borate may be replaced with anaryloxy group such as phenoxide, an alkyloxy group such as methoxide orethoxide, an alkylcarbonyloxy group such as acetate, an arylcarbonyloxygroup such as benzoate, or a halogen atom such as chloride or bromide.

(iii) Quaternary Phosphonium Salts having Aryl and/or Branched AlkylGroups:

Herein usable are compounds of general formulae (15) and (16):

(R¹¹ _(n)PR¹² _(4−n))⁺(X²)⁻  (15)

(R¹¹ _(n)PR¹² _(4−n))⁺ ₂(Y¹)²⁻  (16).

In formulae (15) and (16);

n represents an integer of from 1 to 4.

R¹¹ represents at least one selected from an aryl group and a branchedalkyl group. The branched alkyl group has a structure of “R₃C—”, inwhich R represents at least one selected from a hydrogen atom, an alkylgroup, a substituted alkyl group, an aryl group, and a substituted arylgroup, and at least two of the three R's may be bonded to each other toform a cyclic structure. In this, however, two R's must not be hydrogensat the same time. For example, R¹¹ is a cycloalkyl group, a branchedalkyl group such as an isopropyl or tert-butyl group, or an arylalkylgroup such as a benzyl group.

When n is 2 or more, plural R's may be the same or different ones.

R¹² represents an alkyl group, a substituted alkyl group, an aryl group,or a substituted aryl group.

X² represents a group capable of forming a mono-valent anion, such as ahalogen atom, a hydroxyl group, an alkyloxy group, an aryloxy group,R′COO, HCO₃, (R′O)₂P(═O)O, BR″₄ or the like. In those, R′ represents ahydrocarbon group such as an alkyl group, an aryl group or the like, andtwo (R′O)s may be the same or different ones. R″ represents a hydrogenatom, or a hydrocarbon group such as an alkyl group, an aryl group orthe like, and four R″s may be the same or different ones.

Y¹ represents a group capable of forming a di-valent anion, such as CO₃or the like.

The quaternary phosphonium salts include, for example, the following:

Tetra(aryl or alkyl)phosphonium hydroxides, such astetraphenylphosphonium hydroxide, tetranaphthylphosphonium hydroxide,tetra(chlorophenyl)phosphonium hydroxide, tetra (biphenyl)phosphoniumhydroxide, tetratolylphosphonium hydroxide, tetrahexylphosphoniumhydroxide, etc.;

Mono(aryl or alkyl) triphenylphosphonium hydroxides, such asmethyltriphenylphosphonium hydroxide, ethyltriphenylphosphoniumhydroxide, propyltriphenylphosphonium hydroxide,butyltriphenylphosphonium hydroxide, octyltriphenylphosphoniumhydroxide, tetradecyltriphenylphosphonium hydroxide,benzyltriphenylphosphonium hydroxide, ethoxybenzyltriphenylphosphoniumhydroxide, methoxymethyltriphenylphosphonium hydroxide,acetoxymethyltriphenylphosphonium hydroxide,phenacyltriphenylphosphonium hydroxide, chloromethyltriphenylphosphoniumhydroxide, bromomethyltriphenylphosphonium hydroxide,biphenyltriphenylphosphonium hydroxide, naphtyltriphenylphosphoniumhydroxide, chlorophenyltriphenylphosphonium hydroxide,phenoxyphenyltriphenylphosphonium hydroxide,methoxyphenyltriphenylphosphonium hydroxide,acetoxyphenyltriphenylphosphonium hydroxide,naphtylphenyltriphenylphosphonium hydroxide, etc.;

Mono(aryl)trialkylphosphonium hydroxides, such asphenyltriethylphosphonium hydroxide, biphenyltrimethylphosphoniumhydroxide, phenyltrihexylphosphonium hydroxide,biphenyltrihexylphosphonium hydroxide, etc.

Diaryldialkylphosphonium hydroxides, such as dimethyldiphenylphosphoniumhydroxide, diethyldiphenylphosphonium hydroxide,di(biphenyl)diphenylphosphonium hydroxide, etc.;

Tetraarylphosphonium tetraphenyl borates, such as tetraphenylphosphoniumtetraphenyl borate, tetranaphthylphosphonium tetraphenyl borate,tetra(chlorophenyl)phosphonium tetraphenyl borate,tetra(biphenyl)phosphonium tetraphenyl borate, tetratolylphosphoniumtetraphenyl borate, etc.;

Mono (aryl or alkyl) triphenylphosphonium tetraphenyl borates, such asmethyltriphenylphosphonium tetraphenyl borate, ethyltriphenylphosphoniumtetraphenyl borate, propyltriphenylphosphonium tetraphenyl borate,butyltriphenylphosphonium tetraphenyl borate, octyltriphenylphosphoniumtetraphenyl borate, tetradecyltriphenylphosphonium tetraphenyl borate,benzyltriphenylphosphonium tetraphenyl borate,ethoxybenzyltriphenylphosphonium tetraphenyl borate,methoxymethyltriphenylphosphonium tetraphenyl borate,acetoxymethyltriphenylphosphonium tetraphenyl borate,phenacyltriphenylphosphonium tetraphenyl borate,chloromethyltriphenylphosphonium tetraphenyl borate,bromomethyltriphenylphosphonium tetraphenyl borate,biphenyltriphenylphosphonium tetraphenyl borate,naphtyltriphenylphosphonium tetraphenyl borate,chlorophenyltriphenylphosphonium tetraphenyl borate,phenoxyphenyltriphenylphosphonium tetraphenyl borate,acetoxyphenyltriphenylphosphonium tetraphenyl borate,naphthylphenyltriphenylphosphonium tetraphenyl borate, etc.;

Monoaryltrialkylphosphonium tetraphenyl borates, such asphenyltrimethylphosphonium tetraphenyl borate,biphenyltrimethylphosphonium tetraphenyl borate,phenyltrihexylphosphonium tetraphenyl borate,biphenyltrihexylphosphonium tetraphenyl borate, etc.;

Diaryldialkylphosphonium tetraphenyl borates, such asdimethyldiphenylphosphonium tetraphenyl borate,diethyldiphenylphosphonium tetraphenyl borate,di(biphenyl)diphenylphosphonium tetraphenyl borate, etc.

Apart from the compounds of formula (15) noted above, also employableherein are compounds of formula (16) having a di-valent counter anion.As those, for example, mentioned are quaternary phosphonium salts suchas bis(tetraphenylphosphonium) carbonate,bis(biphenyltriphenylphosphonium) carbonate, as well asbis-tetraphenylphosphonium salt of 2,2-bis(4-hydroxyphenyl)propane, andethylenebis(triphenylphosphonium)dibromide,trimethylenebis(triphenylphosphonium)-bis(tetraphenyl borate), etc.

In addition, further employable herein are compounds of general formulae(17) and (18):

((R₁₃−Ph)_(n)−PPh_((4−n)))⁺(X³)⁻  (17)

((R₁₃−Ph)_(n)−PPh_((4−n)))₂ ⁺(Y²)²⁻  (18)

wherein R¹³ represents an organic group, and plural R¹³'s, if any, maybe the same or different ones; X³ represents a halogen atom, a hydroxylgroup, an alkyloxy group, an aryloxy group, an alkylcarbonyloxy group,an arylcarbonyloxy group, HCO₃, or BR₄ (in which R represents a hydrogenatom or a hydrocarbon group, and four R's may be the same or differentones); Ph represents a phenyl group; Y² represents CO₃; and n representsan integer of from 1 to 4.

Specific examples of those quaternary phosphonium compounds include, forexample, tetraphenylphosphonium hydroxide, biphenyltriphenylphosphoniumhydroxide, methoxyphenyltriphenylphosphonium hydroxide,phenoxyphenyltriphenylphosphonium hydroxide,naphthylphenyltriphenylphosphonium hydroxide, tetraphenylphosphoniumtetraphenyl borate, biphenyltriphenylphosphonium tetraphenyl borate,methoxyphenyltriphenylphosphonium tetraphenyl borate,phenoxyphenyltriphenylphosphonium tetraphenyl borate,naphthylphenyltriphenylphosphonium tetraphenyl borate,tetraphenylphosphonium phenoxide, biphenyltriphenylphosphoniumphenoxide, methoxyphenyltriphenylphosphonium phenoxide,phenoxyphenyltriphenylphosphonium phenoxide,naphthylphenyltriphenylphosphonium phenoxide, tetraphenylphosphoniumchloride, biphenyltriphenylphosphonium chloride,methoxyphenyltriphenylphosphonium chloride,phenoxyphenyltriphenylphosphonium chloride,naphthylphenyltriphenylphosphonium chloride, etc.

Specific examples of branched alkyl-having quaternary phosphoniumsinclude isopropyltrimethylphopshonium, isopropyltriethylphosphonium,isopropyltributylphosphonium, isopropyltriphenylphosphonium,tetraisopropylphosphonium, cyclohexyltriethylphosphonium,cyclohexyltrimethylphosphonium, cyclohexyltributylphosphonium,cyclohexyltriphenylphosphonium, tetracyclohexylphosphonium,1,1,1-triphenylmethyltrimethylphosphonium,1,1,1-triphenylmethyltriethylphosphonium,1,1,1-triphenylmethyltributylphosphonium,1,1,1-triphenylmethyltriphenylphosphonium, etc.

Specific examples of counter anions for X³ include hydroxide,borohydride, tetraphenyl borate, acetate, propionate, fluoride,chloride, hydrocarbonate, etc.

One example of Y² is carbonate.

As specific examples of salts composed of a branched alkyl-havingquaternary phosphonium (cation) and X³ or Y² (anion), mentioned arevarious combinations of the specific examples for cations and anionsnoted above. For those, specifically mentioned areisopropyltrimethylphosphonium hydroxide, cyclohexyltriphenylphosphoniumchloride, 1,1,1-triphenylmethyltriethylphosphonium acetate,bis(isopropyltriethylphosphonium) carbonate, etc.

Of those branched alkyl-having quaternary phosphonium salts, especiallypreferred are cyclohexyltriphenylphosphonium tetraphenyl borate andcyclopentyltriphenylphosphonium tetraphenyl borate, since theircatalytic activity and the quality of polycarbonates to be produced arewell balanced.

It is desirable that the amount of metallic impurities in thephosphorus-containing basic compounds and the quaternary phosphoniumsalts for use in the invention is as small as possible. Especiallypreferably, the amount of alkali metal and alkaline earth metalcompounds in those compounds is not larger than 50 ppm.

[2] Solid-phase Polymerization:

The solid prepolymer prepared previously, which is preferablycrystallized, is further polymerized. The polymerization must beeffected in a poor solvent gas atmosphere.

(i) The poor solvent is meant to indicate that the solubility of theproduct, polycarbonate in it is at most 0.1% by weight. Concretely, itincludes linear aliphatic, branched aliphatic or cycloaliphatichydrocarbons having from 4 to 18 carbon atoms, such as pentane, hexane,heptane, cyclohexane, etc.; ketones suchas acetone, cyclohexanone, etc.;ethers such as dioxane, tetrahydrofuran, etc.; acetonitrile, etc. Ofthose, preferred are linear aliphatic or cycloaliphatic hydrocarbonshaving from 5 to 18 carbon atoms, such as pentane, hexane, heptane,cyclohexane, etc. “In a poor solvent gas atmosphere” as referred toherein is meant to indicate that the polymerization is effected in thepresence of apoor solvent gas such as that mentioned above. Preferably,the poor solvent gas is flowing in some degree through the reactionsystem. In the poor solvent gas atmosphere, the side products, aromaticmonohydroxy compound and diaryl carbonate are easy to remove from thereaction system, and the reaction is accelerated to give polycarbonateshaving an increased molecular weight.

(ii) The shape of the crystalline prepolymer to be subjected to thesolid-phase polymerization is not specifically defined, but theprepolymer is preferably in the form of pellets, beads or the like.

The catalyst for the solid-phase polymerization is aphosphorus-containing basic compound. When the catalyst used in theprepolymerization step is a phosphorus-containing basic catalyst andwhen it remains in the system, the compound could serve as the catalystfor the solid-phase polymerization. If necessary, an additionalphosphorus-containing basic compound serving as the catalyst may beadded to the system, and it may be powdery, liquid or gaseous.

The amount of the catalyst is so controlled that it may be generallyfrom 10⁻⁸ to 10⁻¹ mols, preferably from 10⁻⁷ to 10⁻² mols, morepreferably from 10⁻⁶ to 10⁻³ mols, relative to one mol of the startingdihydroxy compound of the component (A). If its amount is smaller than10⁻⁸ mols, the catalyst could not exhibit its activity. However, iflarger than 10⁻¹ mols, the physical properties of the final product,polycarbonate, especially the heat resistance and the hydrolysisresistance thereof will be degraded, and, in addition, the productioncosts will increase. Adding the catalyst over the defined range ismeaningless.

The polymerization temperature Tp (° C.) and the polymerization time mayvary, depending on various conditions. Preferably, however, theprepolymer is heated at a temperature which is not lower than the glasstransition point of the intended aromatic polycarbonate and at which thecrystalline prepolymer being in solid-phase polymerization is not meltedbut still keeps its solid-phase state, for a period of time fallingbetween 1 minute and 100 hours.

Without being cooled, the thus-obtained, powdery, crystalline aromaticpolycarbonates may be directly introduced into extruders for pelletizingthem, or into shaping machines for shaping them.

[3] In the solid-phase polymerization in the invention, optionally usedis a terminal-stopping agent, preferably p-t-butylphenol, p-cumylphenol,p-phenylphenol or the like. Further if desired, a known branching agentmay also be used. Still if necessary, a known antioxidant may be addedto the reaction system. As the antioxidant, preferred arephosphorus-containing antioxidants.

[4] Oxygen Concentration and Water Concentration in Vapor Phase inPolymerization System:

In the invention, it is desirable that the oxygen concentration in thevapor phase in the polymerization reaction system is not larger than 2ppm. It is also desirable that the water concentration in the reactionsystem is not larger than 2 ppm. The method for lowering the oxygenconcentration in the reaction system to be not larger than 2 ppm and forlowering the water concentration therein also to be not larger than 2ppm is not specifically defined. For example, an oxygen-removing ductequipped with an oxygen filter or the like and a water-removing ductequipped with a moisture filter or the like may be disposed before thepolymerization reactor in the production line.

(4) If desired, the polycarbonates as obtained according to theinvention may be mixed with any known additives of, for example,plasticizers, pigments, lubricating agents, mold-releasing agents,stabilizers, inorganic fillers, etc., before they are used. Further ifdesired, the polycarbonates may be blended with any other polymers, suchas polyolefins, polystyrenes, polyesters, polysulfonates, polyamides,polyphenylene ethers, etc. In particular, they are effectively blendedwith any of polyphenylene ethers, polyether nitrites, terminal-modifiedpolysiloxane compounds, modified polypropylenes, modified polystyrenesand the like having OH, COOH, NH₂ or the like group at their terminals.

EXAMPLES

The invention will be described in more detail with reference to thefollowing Examples and Comparative Examples, which, however, are notintended to restrict the scope of the invention.

In Table 1 below, the viscosity-average molecular weight Mv is obtainedaccording to the following equation, in which [η] indicates the limitingviscosity in methylene chloride at 20° C.

[η]=1.23×10⁻⁵×Mv^(0.83)

In the steam resistance test for polycarbonates, the polycondensatesample to be tested is press-molded into test discs having a thicknessof 1 mm and a diameter of 10 mm, which are then exposed to steam at 121°C. for 48 hours. The decrease in the viscosity-average molecular weight(ΔMv) of the exposed sample is obtained, from which the steam resistanceof the sample is evaluated.

EXAMPLES 1 TO 7

228 g (1 mol) of bisphenol A (BPA), 225 g (1.05 mols) of diphenylcarbonate (DPC) and 0.5 mmols of tetramethylammonium hydroxide (TMAH)were put into a one-liter nickel-steel autoclave equipped with astirrer, and purged with argon five times in all. Next, the mixture washeated at 190° C. and reacted for 30 minutes in the argon atmosphere.Next, this was gradually heated up to 235° C. and reacted for 60 minuteswith being vacuumed up to a vacuum degree of 60 mmHg; then this wasfurther heated gradually up to 270° C. and reacted for 120 minutes withbeing vacuumed up to a vacuum degree of 10 mmHg; then this was stillfurther reacted at that temperature for 30 minutes with being vacuumedup to a vacuum degree of 1 mmHg; and finally, this was still furtherreacted at that temperature for 30 minutes with being vacuumed up to avacuum degree of 0.5 mmHg. After the reaction, the reactor was restoredwith argon to have an atmospheric pressure, and the product, prepolymerformed therein was taken out, and ground.

The prepolymer had a viscosity-average molecular weight of 8800, and itsterminal hydroxyl fraction was 50%. Its melting point measured throughDSC was 226° C.

The thus-obtained prepolymer was dissolved in methylene chloride, towhich was added cyclohexyltriphenylphosphonium tetraphenyl borate (HPTB)in an amount of 1×10⁻⁵ mol/mol-BPA. Next, n-heptane was added thereto togive a powdery deposit. This was concentrated and dried up to solid, andthe solid was further dried in vacuum to obtain a powdery prepolymer.

1.0 g of the powdery prepolymer was charged into a SUS tube having adiameter of 10 mm and a length of 200 mm, and the gas shown in Table 1was introduced thereinto at a flow rate of 100 ml/min at 230° C. In thatcondition, the prepolymer was polymerized in a solid phase for 90minutes to obtain a polycarbonate. The data are shown in Table 1.

Comparative Example 1

The prepolymer having been prepared in the same manner as in Example 1was polymerized in a solid phase also in the same manner as in Example1, except that paraxylene was used herein as the solvent gas. The dataare shown in Table 1. In this, the polycarbonate produced afterpolymerization partly fused.

EXAMPLES 8 TO 14

22.8 g (0.1 mol) of bisphenol A (BPA), 22.5 g (0.105 mols) of diphenylcarbonate (DPC), 0.05 mmols of tetramethylammonium hydroxide (TMAH) and0.001 mmols of tetraphenylphosphonium tetraphenyl borate (TPTB) were putinto a separable 100-liter nickel flask equipped with a stirrer, andpurged with argon five times in all. Next, the mixture was heated at190° C. and reacted for 30 minutes in the argon atmosphere. Next, thiswas gradually heated up to 235° C. and reacted for 60 minutes with beingvacuumed up to a vacuum degree of 60 mmHg; then this was further heatedgradually up to 270° C. and reacted for 120 minutes with being vacuumedup to a vacuum degree of 10 mmHg; then this was still further reacted atthat temperature for 30 minutes with being vacuumed up to a vacuumdegree of 1 mmHg; and finally, this was still further reacted at thattemperature for 30 minutes with being vacuumed up to a vacuum degree of0.5 mmHg. After the reaction, the reactor was restored with argon tohave an atmospheric pressure, and the product, prepolymer formed thereinwas taken out, and ground.

The prepolymer had a viscosity-average molecular weight of 8300, and itsterminal hydroxyl fraction was 50%. Its melting point measured throughDSC was 226° C.

The thus-obtained prepolymer was dissolved in methylene chloride, towhich was added n-heptane was to give a powdery deposit. This wasconcentrated and dried up to solid, and the solid was further dried invacuum to obtain a powdery prepolymer. 0.2 g of the powdery prepolymerwas charged into a SUS tube having a diameter of 10 mm and a length of200 mm, and the gas shown in Table 1 was introduced thereinto at a flowrate of 100 ml/min at 90 ° C. In that condition, the prepolymer waspolymerized in a solid phase for 90 minutes to obtain a polycarbonate.

The data are shown in Table 1.

Comparative Example 2

The prepolymer having been prepared in the same manner as in Example 8was polymerized in a solid phase in the same manner as in Example 1,except that paraxylene was used herein as the solvent gas. The data areshown in Table 1. In this, the polycarbonate produced afterpolymerization partly fused.

Comparative Example 3

The prepolymer having been prepared in the same manner as in Example 1was polymerized in a solid phase in the same manner as in Example 1,except that 1×10⁻⁴ mol/mol-BPA of triethylamine was used as the solventherein in place of 1×10⁻⁵ mol/mol-BPA of cyclohexyltriphenylphosphoniumtetraphenyl borate (HPTB).

The data are shown in Table 1.

Comparative Example 4

The prepolymer having been prepared in the same manner as in Example 1was polymerized in a solid phase in the same manner as in Example 1,except that 1×10⁻⁴ mol/mol-BPA of 4-dimethylaminopyridine was used asthe solvent herein in place of 1×10⁻⁵ mol/mol-BPA ofcyclohexyltriphenylphosphonium tetraphenyl borate (HPTB).

The data are shown in Table 1.

TABLE 1 Poor Viscosity-Average Steam Catalyst Solvent Molecular WeightResistance Test Compound Compound (Mv) (ΔMv) Example 1 HPTB pentane39,400 100 Example 2 HPTB hexane 35,900 100 Example 3 HPTB cyclohexane40,100 100 Example 4 HPTB heptane 36,700 100 Example 5 HPTB octane33,100 200 Example 6 HPTB decane 38,300 200 Example 7 HPTB undecane27,700 200 Example 8 TPTB pentane 30,400 200 Example 9 TPTB hexane27,800 200 Example 10 TPTB cyclohexane 29,700 200 Example 11 TPTBheptane 30,400 100 Example 12 TPTB octane 25,100 200 Example 13 TPTBdecane 22,900 200 Example 14 TPTB undecane 18,600 200 ComparativeExample 1 HPTB paraxylene 15,800 200 Comparative Example 2 TPTBparaxylene 13,100 300 Comparative Example 3 trimethyl-amine pentane 8,330 — Comparative Example 4 4-dimethyl- pentane  9,730 —amino-pyridine notes HPTB: cyclohexyltriphenylphosphonium tetraphenylborate TPTB: tetraphenylphosphonium tetraphenyl borate

INDUSTRIAL APPLICABILITY

According to the invention, efficiently produced are high-qualitypolycarbonates having a high molecular weight.

What is claimed is:
 1. A process for producing a polycarbonate, whichcomprises preparing a polycarbonate prepolymer through prepolymerizationfollowed by polymerizing the prepolymer in a solid phase in the presenceof a phosphorus-containing basic compound serving as a catalyst in anatmosphere of a poor solvent gas selected from the group consisting of alinear aliphatic hydrocarbon having from 5 to 18 carbon atoms andcycloaliphatic hydrocarbon having from 5 to 18 carbon atoms.
 2. Theprocess for producing a polycarbonate as claimed in claims 1, whereinthe phosphorus-containing basic compound is a quaternary phosphoniumsalt.